MIAMI -- For the first few minutes of Game 2 of the Eastern Conference finals, it appeared the Boston Celtics could be in some trouble.

They left Miami's shooters open for three quick 3-pointers. They allowed the Heat to get multiple second chance opportunities. Robert Williams looked uncomfortable defending in space and Miami kept making him -- and Boston -- pay.

But then, at the 5 minute, 14 second mark of the first quarter, Grant Williams checked into the game. And, from that point forward, this game -- and this series--- fundamentally changed.

Boston absolutely scorched Miami over the final 17 minutes of the first half, going on a 57-27 run while Williams never left the floor en route to a 127-102 victory in front of a shell-shocked sellout crowd here at FTX Arena.

The win evened the series at a game apiece.

"He just [has come] a long way from his first year," said Celtics forward Jayson Tatum, who led the Celtics with 27 points, said of Grant Williams. "He's worked on his game, and he's developed into somebody that we believe and trust in to catch it at half court.

"He sees an opening, takes it to the hole, makes the right play. That's what he did."

Boston spent the little less than 48 hours between the end of its Game 1 loss to Miami Tuesday night and tip-off of Game 2 Thursday expressing quiet confidence in its ability to bounce back. The Celtics could point to winning three of the four quarters in the first game, losing thanks to being outscored 39-14 in a truly disastrous third quarter.

They also got back a pair of starters in Marcus Smart and Al Horford, who missed Game 1 because of a midfoot sprain and being in the NBA's health and safety protocols, respectively.

But things didn't truly click into place for the Celtics until Boston went away from the starting five that had been a dominant five-man unit all season midway through the first quarter. The Celtics had begun to climb back into things following a quick timeout by Ime Udoka but it was Grant Williams -- who had started the prior four games -- arriving on the scene that dumped rocket fuel into Boston's play at both ends of the court.

"They came out and hit us in the mouth and we didn't know how to respond," Heat center Bam Adebayo said.

Suddenly, the Celtics were flying around at both ends of the court. They were spacing the floor offensively, hitting 9-of-11 shots from 3-point range in the first quarter alone. They scrambled to Miami's shooters, forcing them to go 2-for-8 over the final few minutes of the first and 3-for-15 over the final 20 minutes of the first half.

By the time the damage was done, Boston led 70-45 at halftime and the final 24 minutes were nothing more than an elementary exercise needed to ensure this series headed back to Boston tied up.

"Spaced the floor well," Celtics coach Ime Udoka said of why those lineups were so effective. "We got to attack some match-ups that we wanted to and space out Adebayo and [PJ] Tucker and some of those guys. Obviously with Rob in there, he has his things that he does well but he has some limitations as well as far as spacing the court.

"We saw success against Milwaukee and Brooklyn doing that with Al and Grant lineups where they can space it out and we can attack multiple ways. So [it created] a lot of open shots, a lot of open threes and he got going, but also opened up the lanes for our drivers."

It certainly didn't hurt that Smart returned and had a virtuoso performance at both ends of the court. While he is renowned for his defense, and earned plaudits for it by snapping up the NBA's Defensive Player of the Year award earlier this month, it was his offense -- and, specifically, his calming influence on Boston -- that was missed in Game 1.

With their point guard back on the court, the Celtics went from committing 19 turnovers in Game 1 to just 10 in Game 2 for a total of nine Heat points. Smart, meanwhile, finished with 24 points, nine rebounds and 12 assists with just one turnover in 40 minutes.

The Celtics, meanwhile, shot 51 percent from the field overall and drilled 20 of their 40 3-point attempts.

"[I take] a lot of pride," Smart said of his point guard play. "That's what I've been doing my whole career. That's what I got drafted here to do. I just waited my turn. I'm blessed to be in the situation I am to have the opportunity to go out and show what I can do, and I think everybody in the organization, in the world, is seeing what I can do at that point guard position."

Boston's first half dominance was far from just at the offensive end and it was no coincidence it took place with Smart and Horford, one of its most versatile defensive big men, back on the court.

In that dominant first half, Miami was 0-for-4 with four turnovers when Horford was the primary defender, per ESPN's Stats and Information research. Smart, meanwhile, was the last defender on Jimmy Butler -- who demolished Boston with Smart sidelined in Game 1 -- on 28 of the 46 plays Butler was on the court. Butler took just four shots when Smart guarded him.

And while Butler had another strong game, finishing with 29 points on 11-for-18 shooting, he took just eight free throws compared to 18 in Game 1.

"Jimmy is a warrior, man," Smart said. "Jimmy has been doing this for a long time. He understands the game. He understands his strengths. He understands his team's strengths. So when you have a guy who has an IQ like Jimmy, it's always going to be a tough matchup.

"For me my assignment was just to make everything tough for him. We knew he was going to hit some shots. If he did, he had to work for them. That's just where I came in."

The result was Miami was left scrambling to pick up the pieces. The Heat have now won a single quarter through the first eight in this series -- that decisive 3rd quarter of Game 1 -- and have been outscored by 36 points across the other seven.

To make matters worse, P.J. Tucker left the game in the third quarter with a left knee contusion and did not return -- while Kyle Lowry sat out his fourth straight game with a left hamstring strain.

"Ask him," Heat coach Erik Spoelstra said about Tucker, "and he's good to go."

Boston knows its work is far from done. The Celtics alternated wins and losses with the Milwaukee Bucks for the first six games of the Eastern Conference semifinals before finally winning a second straight game to close the series out Sunday in Game 7 at TD Garden.

But as things shift back to Boston for Game 3 Saturday night, the Celtics are fully aware of the fact that they don't have the same luxury this time around against the top-seeded Heat.

"They tried to embarrass us," Butler said. "They did embarrass us. So I think we got to realize that -- use it as fuel, whatever you want to say -- but realize that the game can get out of hand whenever you're playing against a really good team like them, that can score the ball and get stops.

"We got a tough job to do to go over there and win. But if they did it, we can do it as well."